Tensile properties and self-healing mechanism of pre-cracked UHPC under different curing environments

This study investigates the effects of curing environments, age, and initial crack width on the self-healing performance of pre-cracked UHPC. Direct tensile tests were conducted using crack width as a quantitative index for damage and healing. Results showed significant recovery in tensile strength, with all specimens surpassing the control group after 56 days. Single fiber pull-out tests revealed temperature-dependent interfacial effects: a 60 °C water bath enhanced secondary hydration but also accelerated steel fiber corrosion, altering the failure mode from pull-out to fracture. Microstructural changes were examined via thermal analysis, X-CT, and SEM, confirming that water baths promoted hydration and densification. However, surface crack healing hindered internal hydration by limiting moisture and CO₂ ingress. A multi-scale analysis linked macroscopic tensile recovery to microscopic mechanisms. Additionally, a theoretical model based on hydration kinetics and the Arrhenius equation was proposed to estimate healable crack width, providing predictions that aligned well with experimental data.